Orientation-Dependent Mechanical Response and Composite Action of Rectangular Pultruded GFRP Profiles and Integrated Sandwich Panels

Pultruded glass fibre-reinforced polymer (GFRP) profiles are promising structural cores for lightweight sandwich panels, but their strong longitudinal response is accompanied by weak transverse resistance and local web instability. A matched experimental programme examined rectangular hollow pultruded GFRP profiles and vacuum-infused sandwich panels under four-point bending, short-span three-point bending and flatwise compression in H and V orientations. Changing from H to V increased the peak loads of individual profiles by 9.35% in four-point bending and by 26.06% in short-span loading but reduced the flatwise compressive peak load by 30.12%. For integrated panels, the same reorientation increased the four-point bending peak load by 22.74%, caused only a marginal change in short-span capacity and reduced the flatwise compressive peak load by 28.24%. Failure involved local web buckling, web shear damage, longitudinal splitting, laminate delamination and interfacial debonding. Continuous face sheets and wrapping laminates restrained local deformation and contributed to substantial post-damage resistance, consistent with load redistribution within the integrated section. Relative to a baseline comprising three individual profiles and the corresponding hollow FRP reference panel, integrated-panel capacities increased by 15.76%, 37.71% and 78.44% under four-point bending, short-span loading and flatwise compression, respectively. These results identify profile orientation and transverse web stability as key design parameters for pultruded-profile-core sandwich panels.